1. Field of the Invention
The present invention relates to a process for producing a high resilience polyurethane foam by reacting a polyol with a polyisocyanate in the presence of a catalyst, a blowing agent, and a foam stabilizer.
2. Description of the Background
High resilience polyurethane foams are widely used for a variety of articles such as automotive seating, furniture, bedding, and the like.
Heretofore, in production of high resilience polyurethane foams, toluene diisocyanate (hereinafter referred to as TDI), or a mixture of TDI with diphenylmethane diisocyanate (hereinafter referred to as MDI) has been used as the starting isocyanate. However, the TDI has disadvantages of high vapor pressure, high toxicity, and intolerably offensive odor, which aggravate working environments. The TDI has further a disadvantage of low reactivity with a starting polyol, which decreases the productivity and increases the plant investment.
To solve the above disadvantages caused by TDI, use of MDI and/or modified MD for high resilience polyurethane foams is disclosed in Japanese Laid-Open Patent Application Nos. 53-51299, 57-109820, and 62-112616, for example.
A polyurethane foam produced from MDI and/or modified MDI as the base materials is generally called "all-MDI high resilience polyurethane foam", which has excellent characteristics of superior foam properties, low toxicity to facilitate maintenance of a safe working environment at a production site, and also high production speed to increase productivity, for example.
On the other hand, the all-MDI high resilience polyurethane formulations involve serious problems. For example, the flow properties of the system-liquid and the flowability of foams are extremely poor so that low density of the foam cannot easily be attained. Accordingly, the lowering of foam density without impairing liquid flow characteristics or foam flowability is attained by using, as a blowing agent, a halogenated hydrocarbon such as trichloromonofluoromethane (hereinafter referred to as CFC-11) in an amount of from 5 to 15 parts by weight based on the polyol. However, this is still unsatisfactory, and further improvement is necessary in the starting material formulation and the production technique to attain a mopre reduced density of the all-MDI high resilience polyurethanes.
Regarding the halogenated hydrocarbons, the use of chlorofluorocarbons like CFC-11, which may destroy the ozone layer surrounding the earth, has attracted world-wide concern. This concern has prompted a reduction in the amount of use, however further reduction and increased regulation appear necessary.
In producing the all-MDI high resilience polyurethane foam, an urgent and newest problem is the need to reduce the amount of a chlorofluorocarbon (hereinafter referred to as CFC) as a blowing agent and to use more water instead.
On the other hand, "CFC-substituting compounds" such as methylene chloride, dichlorotrifluoroethane, and dichloromonofluoroethane (hereinafter referred to as HCFC-123, and HCFC-141b, respectively) have been proposed as substitutes for the CFC compounds such a CFC-11 which may destroy the ozone layer. However, these CFC-substituting compounds still have the implicit possibility of destroying the ozone layer, and, moreover, are expensive in comparison with the conventionally used CFC compounds. Therefore, the CFC-substituting compounds also cannot be used at the same high level. Further, this would also be undesirable from an economical point of view. Therefore, an improved formulation is strongly desired in which the amount of the CFC compound is decreased and, instead, the amount of water as a blowing agent is increased.
The use of water as a blowing agent in a larger amount, unfortunately, poses several technical problems such that foams become far less stable, thereby causing the phenomena of settling (in other words recession) and the like in the foaming process with the processing range being narrowed and with the properties of the foam being deteriorated. Thus, a low density of the foam is attained with extreme difficulty; and the moldability of the foam is inevitably impaired causing blistering of the foam surface and with the added liability of void build-up.
The conventionally used catalysts for all-MDI high resilience polyurethane foams are amine catalysts such as triethylenediamine as a base catalyst with bis(2-dimethylaminoethyl)ether or dimethylethanolamine as a cocatalyst. This amine catalyst system is not capable of lowering the density of a foam which employs conventionally used CFC compounds as the blowing agent, and will not give a practically useful high resilience polyurethane foam of low density when a blowing agent system of a decreased amount of CFC compound and an increased amount of water is used.
Thus, a need continues to exist for a process for producing a high resilience polyurethane foam, which foam is of a reduced density, and which process uses a reduced amount of chlorofluorocarbons (CFC).